Superantigen YPMa Exacerbates the Virulence ofYersinia pseudotuberculosisin Mice

Abstract

The gram-negative bacterium Yersinia pseudotuberculosis is widely spread in nature and is responsible for sporadic infection in many animal species (10). Humans are commonly infected after ingestion of food or water contaminated with excreta of infected animals. Y. pseudotuberculosis causes acute ileitis and mesenteric lymphadenitis, sometimes complicated by septicemia (10, 26), but is also responsible for the occurrence of postinfection complications such as reactive arthritis and erythema nodosum (10,35,45,46). This microorganism has been suggested as one of the causative agents of Kawasaki syndrome, an acute, self-limited vasculitis affecting predominantly infants and young children (4,25,39). A few years ago, Y. pseudotuberculosis strains producing a mitogen activity were isolated from a mass outbreak in Japan (48) and from a patient with Kawasaki-like symptoms (1, 51). The substance, purified from bacterial lysates and exhibiting a mitogenic activity on human peripheral blood mononuclear cells (PBMC), was first designated YPM, for Y. pseudotuberculosis-derived mitogen (30), and then YPMa after the discovery of a variant (36). YPMa was characterized as a 14.5-kDa superantigenic toxin activating human T lymphocytes bearing T-cell receptors exhibiting the V␤3, V␤9, V␤13.1, and V␤13.2 variable regions (1, 48). The geographic distribution of the 456-bp superantigenencoding gene ypmA is rather heterogeneous, being present in most Y. pseudotuberculosis strains from the Far East but only in about 20% of European clinical isolates (13,52).A recent study showed that 61% of patients acutely infected with Y. pseudotuberculosis, especially those with systemic complications, had elevated anti-YPM immunoglobulin G level in blood, thereby demonstrating the production of YPMa in vivo (2). Furthermore, V␤3-bearing T cells were increased in patients during the acute phase of the disease (2). Additionally, Miyoshi-Akiyama et al. (32) found that purified YPMa was able to induce lethal shock in a murine experimental model, demonstrating the toxicity of the Y. pseudotuberculosis superantigenic toxin in vivo. The toxin was also found to alter in vitro epithelial function by reducing active ion transport and increasing epithelial permeability (16). Altogether, these data suggest a role of YPMa in the pathogenesis of Y. pseudotuberculosis infections, but experimental evidence necessary to confirm this hypothesis is lacking. In this study, we constructed a superantigen-deficient mutant of Y. pseudotuberculosis and tested its virulence in a mouse experimental model of infection. Rodents have been extensively used as the animal model to study Yersinia infections since they develop a disease resembling yersiniosis in humans (22). We found that inactivation of ypmA reduced the virulence of Y. pseudotuberculosis after intravenous (i.v.) challenge but not after intragastric (i.g.) inoculation, demonstrating an exacerbated toxicity of YPMa-producing Y. pseudotuberculosis in systemic infection. MATERIALS AND METHODSBacterial strains, growth ...

The pmrF polymyxin-resistance operon of Yersinia pseudotuberculosis is upregulated by the PhoP-PhoQ two-component system but not by PmrA-PmrB, and is not required for virulence

“…Y. pseudotuberculosis, S. typhimurium and E. coli strains were grown at 28 uC, 37 uC and 37 uC, respectively, in Luria-Bertani (LB) broth or on agar plates. Mating experiments between E. coli and Y. pseudotuberculosis were plated on M9 minimum medium agar, as described previously (Carnoy et al, 2000). Ampicillin (100 mg ml ) and sucrose (10 %) were added to media for bacterial selection when necessary.…”

“…Animals were kept in positive-pressure cabinets during experimentation, and mortality was monitored daily for 21 days after challenge. For each experimental infection, the presence of the virulence plasmid pYV was confirmed by PCR on bacterial thermolysates using primers YOPH1 and YOPH2, which are internal to yopH, a gene located on pYV (Carnoy et al, 2000). Infected animals were monitored for 3 weeks, and the 50 % lethal dose (LD 50 ) was calculated from groups of 5 (i.v.…”

Geographical Heterogeneity between Far Eastern and Western Countries in Prevalence of the Virulence Plasmid, the SuperantigenYersinia pseudotuberculosis-Derived Mitogen, and the High-Pathogenicity Island amongYersinia pseudotuberculosisStrains

“…Y. pseudotuberculosis is also known to produce a superantigenic toxin, known as YPM (1,46) and then YPMa after the discovery of a variant (36). It was experimentally confirmed that YPMa is a virulence factor which exacerbates the toxicity of Y. pseudotuberculosis in systemic but not in gastroenteric infection in mice (11). Superantigen-producing strains could be separated into three clusters which contained YPMa, YPMb, or YPMc encoded by the ypmA, ypmB (36), and ypmC (10) genes, respectively.…”

The Superantigen GeneypmIs Located in an Unstable Chromosomal Locus ofYersinia pseudotuberculosis

“…This molecule (designated YPM for Y. pseudotuberculosis-derived mitogen) is a 14.5-kDa protein able to induce proliferation of human T lymphocytes bearing V␤3, V␤9, V␤13.1, and V␤13.2 T-cell receptor variable regions (1,61). In vivo, YPM induces lethal shock in mice (44) and exacerbates the virulence of Y. pseudotuberculosis in a murine experimental model of systemic infection (13). To date, three YPM variants (YPMa, YPMb, and YPMc) have been described.…”